Difference between subdivide smooth and multiresolution?
Reference Link
https://docs.blender.org/manual/en/dev/modeling/modifiers/generate/multiresolution.html

DESCRIPTION
The Multiresolution Modifier (often shortened to “Multires”) gives you the ability to subdivide a mesh similarly to the Subdivision Surface Modifier, but also allows you to edit the new subdivision levels in sculpt mode.

To Conclude:
Multiresolution modifier is used when you want to do 3d brush sculpting work. As you sculpt from low resolution and progress to higher resolution the modifier allow you to step up your mesh resolution. Example of such models are cloth, faces, landscapes or fine details.

For the regular subdivide its used for subviding models that does not require sculpting. Often used along with box modeling technique where you start your model with a regular box or single polygon plane. Usually applied on models like cars, planes or any hard surface models.

Hope that answer your question.